Coming over every so often to cheer her up (5)
I believe the answer is:
erect
'up' is the definition.
(I've seen this in another clue)
'coming over every so often to cheer her' is the wordplay.
'coming over' shows that the letters should be reversed in order.
'every so often' means one should take alternating letters.
'to'+'cheer'+'her'='tocheerher'
The alternate letters of 'tocheerher' are 'tcere'.
'tcere' in reverse letter order is 'ERECT'.
(Other definitions for erect that I've seen before include "Build, put up" , "Upright; put up" , "Build, upright" , "Construct - perpendicular" , "Upright or vertical" .)